* Re: Raid5 to another raid level??
@ 2011-09-07 16:26 Michael Busby
[not found] ` <CAFsPQ__YdDnJw=qgLAq10vRbNPy4B_EhkV4FU0JAfovxnw9TxQ@mail.gmail.com>
0 siblings, 1 reply; 17+ messages in thread
From: Michael Busby @ 2011-09-07 16:26 UTC (permalink / raw)
To: neilb; +Cc: john.robinson, linux-raid
Thanks for taking the time to respond, I am now running a 4 disk raid5
soon to be upgraded to a 8 disk raid6
-- Sent from my HP TouchPadOn 7 Sep 2011 02:08, <neilb@suse.de> wrote:
On Fri, 2 Sep 2011 14:11:57 +0100 Michael Busby <michael.a.busby@gmail.com>
wrote:
> I am using the 3.0.0 kernel so that should not be a issue, have just
> upgraded mdadm on my box to 3.2.2 from 3.1.4
>
> would i be right in thinking that to get from raid0 to raid5 i would
> first have to change from raid0 to raid4 and add the extra disk for
> parity, once i am at this level i would need a command to get the
> parity data striped over the raid5 and not in a single disk like raid4
> or maybe there is a way to go from raid0 direct to raid5 by adding the
> extra disk and then having the parity data created and spread over the
> disks....
(I vaguely recall already replying to this but find no evidence - apologies
if this is a duplicate).
RAID0 to RAID5 does happen in two stages but only one rebuild is needed.
mdadm should make it all 'just work'.
i.e.
mdadm -G /dev/md0 -l 5 --raid-devices=4 --add /dev/sdf \
--backup-file=/root/md0-backup
This will:
- convert the array from RAID0 to RAID5 in a 'parity-last' layout, which
is really the same thing as RAID4.
- 'freeze' recovery
- add /dev/sdf as a spare
- request a reshape to change the layout from 'parity-last' to
'left-symetric'
- 'unfreeze' recovery
Then the kernel will notice that a reshape is needed and allowed, will add
the spare and start reshaping the array and creating parity at the same time.
So you don't need an intermediate state of a complete RAID4 - a degraded
RAID4 is sufficient and handled automatically.
NeilBrown
>
> On 2 September 2011 13:49, NeilBrown <neilb@suse.de> wrote:
> > On Fri, 2 Sep 2011 11:35:30 +0100 Michael Busby <michael.a.busby@gmail.com>
> > wrote:
> >
> >> Great, will test that in a bit
> >>
> >> will mdadm 3.2.2 support converting raid4 to raid5
> >>
> >> "A RAID4 can change the number of devices or the size of individual
> >> devices. It cannot be converted to RAID5 yet (though that should be
> >> trivial to implement)"
> >
> > I guess the man page needs updating. You would need a reasonably recent
> > kernel... 2.6.30 or later. I guess that isn't so recent any more.
> >
> > NeilBrown
> >
> >
> >>
> >> On 2 September 2011 11:22, NeilBrown <neilb@suse.de> wrote:
> >> > On Fri, 2 Sep 2011 10:12:32 +0100 Michael Busby <michael.a.busby@gmail.com>
> >> > wrote:
> >> >
> >> >> Thanks Neil
> >> >>
> >> >> Is there anyway back from raid0 to raid4 as i know once at raid0 i
> >> >> will no longer be able to add any disks, in theory i could change
> >> >> echo raid0 > /sys/block/md0/md/level,but this would require adding a
> >> >> missing disk to the raid4 at the same time, not sure how easy that
> >> >> would be todo
> >> >>
> >> >
> >> > Yes, you can switch from RAID0 to RAID4 in much the same way as you switch
> >> > from RAID4 to RAID0.
> >> > You can then freeze/add-disk/change-size/unfreeze/wait/switch-back-to-RAID0
> >> > to add more devices.
> >> >
> >> > mdadm-3.2.2 should be able to do all this for you. i.e. you ask it to --grow
> >> > a RAID and --add some disks at the same time, and it will do all the required
> >> > magic.
> >> >
> >> > This hasn't been tested extensively, but should work in simple cases.
> >> >
> >> > Of course the more devices you have in a RAID0, the less reliability you have
> >> > - but e.g. as a cache for a tape backup system a large RAID0 is fine.
> >> >
> >> > NeilBrown
> >> >
> >> >
> >> >
> >
> >
--
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^ permalink raw reply [flat|nested] 17+ messages in thread* Re: Raid5 to another raid level??
@ 2011-09-01 23:50 Michael Busby
2011-09-02 0:54 ` Michael Busby
0 siblings, 1 reply; 17+ messages in thread
From: Michael Busby @ 2011-09-01 23:50 UTC (permalink / raw)
To: john.robinson; +Cc: linux-raid
Will test tomorrow once back in the office, hope the 4tb sync will be
finished by then
I will report back my findings
-- Sent from my HP TouchPadOn 1 Sep 2011 11:34 PM,
<john.robinson@anonymous.org.uk> wrote:
On 01/09/2011 22:50, Michael Busby wrote:
> I have found the following and see that you can convert from raid4 to
> raid0 fairly easy
>
>
> http://ubuntuforums.org/showpost.php?p=10412231&postcount=20
>
> i have a 2 disk raid5 and want to be able to convert this to raid0, i
> was thinking of adding a extra 2 disk and setting them up as raid0,
> moving the data over then adding the original raid5 disks to the raid0
> setup, but i see that you are unable to add disk to a raid0 setup,
> would it be possible to setup a raid4 with 2 disks and 1 missing, move
> the data from the raid5 to raid4 then add both of the original disks
> to the raid4 the downgrade this to raid0???
Off the top of my head, feeling slightly sozzled (been for a few beers),
this might work, but as your linked post referring to a list reply from
Neil Brown says, you should test first. You could use some USB sticks,
or alternatively loopback devices are ideal for this kind of test.
Cheers,
John.
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Raid5 to another raid level??
2011-09-01 23:50 Michael Busby
@ 2011-09-02 0:54 ` Michael Busby
2011-09-02 2:19 ` NeilBrown
0 siblings, 1 reply; 17+ messages in thread
From: Michael Busby @ 2011-09-02 0:54 UTC (permalink / raw)
To: john.robinson; +Cc: linux-raid
As could not sleep, have just tested and works fine...here is what i have done
sdd and sde are the 2 new disks
mdadm -C /dev/md1 -l4 -n3 -e 1.0 /dev/sdd /dev/sde missing
not sure if worth now using 1.2 as this seems the default setting if
not specified??
sdb and sdc are the old raid 5 disks
echo frozen > /sys/block/md0/md/sync_action
mdadm /dev/md0 --add /dev/sdb
mdadm --grow --force /dev/md0 --raid-disks=4
echo frozen > /sys/block/md0/md/sync_action
mdadm /dev/md0 --add /dev/sdc
mdadm --grow --force /dev/md0 --raid-disks=5
echo raid0 > /sys/block/md0/md/level
then resize the fs...job done :)
On 2 September 2011 00:50, Michael Busby <michael.a.busby@gmail.com> wrote:
> Will test tomorrow once back in the office, hope the 4tb sync will be
> finished by then
>
> I will report back my findings
>
>
>
> -- Sent from my HP TouchPadOn 1 Sep 2011 11:34 PM,
> <john.robinson@anonymous.org.uk> wrote:
> On 01/09/2011 22:50, Michael Busby wrote:
>> I have found the following and see that you can convert from raid4 to
>> raid0 fairly easy
>>
>>
>> http://ubuntuforums.org/showpost.php?p=10412231&postcount=20
>>
>> i have a 2 disk raid5 and want to be able to convert this to raid0, i
>> was thinking of adding a extra 2 disk and setting them up as raid0,
>> moving the data over then adding the original raid5 disks to the raid0
>> setup, but i see that you are unable to add disk to a raid0 setup,
>> would it be possible to setup a raid4 with 2 disks and 1 missing, move
>> the data from the raid5 to raid4 then add both of the original disks
>> to the raid4 the downgrade this to raid0???
>
> Off the top of my head, feeling slightly sozzled (been for a few beers),
> this might work, but as your linked post referring to a list reply from
> Neil Brown says, you should test first. You could use some USB sticks,
> or alternatively loopback devices are ideal for this kind of test.
>
> Cheers,
>
> John.
>
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Raid5 to another raid level??
2011-09-02 0:54 ` Michael Busby
@ 2011-09-02 2:19 ` NeilBrown
2011-09-02 9:12 ` Michael Busby
0 siblings, 1 reply; 17+ messages in thread
From: NeilBrown @ 2011-09-02 2:19 UTC (permalink / raw)
To: Michael Busby; +Cc: john.robinson, linux-raid
On Fri, 2 Sep 2011 01:54:49 +0100 Michael Busby <michael.a.busby@gmail.com>
wrote:
> As could not sleep, have just tested and works fine...here is what i have done
>
> sdd and sde are the 2 new disks
>
> mdadm -C /dev/md1 -l4 -n3 -e 1.0 /dev/sdd /dev/sde missing
>
> not sure if worth now using 1.2 as this seems the default setting if
> not specified??
>
> sdb and sdc are the old raid 5 disks
>
> echo frozen > /sys/block/md0/md/sync_action
> mdadm /dev/md0 --add /dev/sdb
> mdadm --grow --force /dev/md0 --raid-disks=4
>
> echo frozen > /sys/block/md0/md/sync_action
> mdadm /dev/md0 --add /dev/sdc
> mdadm --grow --force /dev/md0 --raid-disks=5
You can do all this in one step - 3 to 5.
> echo frozen > /sys/block/md0/md/sync_action
> mdadm /dev/md0 --add /dev/sdb
> mdadm /dev/md0 --add /dev/sdc
> mdadm --grow --force /dev/md0 --raid-disks=5
NeilBrown
>
> echo raid0 > /sys/block/md0/md/level
>
> then resize the fs...job done :)
>
>
>
> On 2 September 2011 00:50, Michael Busby <michael.a.busby@gmail.com> wrote:
> > Will test tomorrow once back in the office, hope the 4tb sync will be
> > finished by then
> >
> > I will report back my findings
> >
> >
> >
> > -- Sent from my HP TouchPadOn 1 Sep 2011 11:34 PM,
> > <john.robinson@anonymous.org.uk> wrote:
> > On 01/09/2011 22:50, Michael Busby wrote:
> >> I have found the following and see that you can convert from raid4 to
> >> raid0 fairly easy
> >>
> >>
> >> http://ubuntuforums.org/showpost.php?p=10412231&postcount=20
> >>
> >> i have a 2 disk raid5 and want to be able to convert this to raid0, i
> >> was thinking of adding a extra 2 disk and setting them up as raid0,
> >> moving the data over then adding the original raid5 disks to the raid0
> >> setup, but i see that you are unable to add disk to a raid0 setup,
> >> would it be possible to setup a raid4 with 2 disks and 1 missing, move
> >> the data from the raid5 to raid4 then add both of the original disks
> >> to the raid4 the downgrade this to raid0???
> >
> > Off the top of my head, feeling slightly sozzled (been for a few beers),
> > this might work, but as your linked post referring to a list reply from
> > Neil Brown says, you should test first. You could use some USB sticks,
> > or alternatively loopback devices are ideal for this kind of test.
> >
> > Cheers,
> >
> > John.
> >
> --
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Raid5 to another raid level??
2011-09-02 2:19 ` NeilBrown
@ 2011-09-02 9:12 ` Michael Busby
2011-09-02 10:22 ` NeilBrown
0 siblings, 1 reply; 17+ messages in thread
From: Michael Busby @ 2011-09-02 9:12 UTC (permalink / raw)
To: NeilBrown; +Cc: john.robinson, linux-raid
Thanks Neil
Is there anyway back from raid0 to raid4 as i know once at raid0 i
will no longer be able to add any disks, in theory i could change
echo raid0 > /sys/block/md0/md/level,but this would require adding a
missing disk to the raid4 at the same time, not sure how easy that
would be todo
On 2 September 2011 03:19, NeilBrown <neilb@suse.de> wrote:
> On Fri, 2 Sep 2011 01:54:49 +0100 Michael Busby <michael.a.busby@gmail.com>
> wrote:
>
>> As could not sleep, have just tested and works fine...here is what i have done
>>
>> sdd and sde are the 2 new disks
>>
>> mdadm -C /dev/md1 -l4 -n3 -e 1.0 /dev/sdd /dev/sde missing
>>
>> not sure if worth now using 1.2 as this seems the default setting if
>> not specified??
>>
>> sdb and sdc are the old raid 5 disks
>>
>> echo frozen > /sys/block/md0/md/sync_action
>> mdadm /dev/md0 --add /dev/sdb
>> mdadm --grow --force /dev/md0 --raid-disks=4
>>
>> echo frozen > /sys/block/md0/md/sync_action
>> mdadm /dev/md0 --add /dev/sdc
>> mdadm --grow --force /dev/md0 --raid-disks=5
>
> You can do all this in one step - 3 to 5.
>
>> echo frozen > /sys/block/md0/md/sync_action
>> mdadm /dev/md0 --add /dev/sdb
>> mdadm /dev/md0 --add /dev/sdc
>> mdadm --grow --force /dev/md0 --raid-disks=5
>
> NeilBrown
>
>
>
>>
>> echo raid0 > /sys/block/md0/md/level
>>
>> then resize the fs...job done :)
>>
>>
>>
>> On 2 September 2011 00:50, Michael Busby <michael.a.busby@gmail.com> wrote:
>> > Will test tomorrow once back in the office, hope the 4tb sync will be
>> > finished by then
>> >
>> > I will report back my findings
>> >
>> >
>> >
>> > -- Sent from my HP TouchPadOn 1 Sep 2011 11:34 PM,
>> > <john.robinson@anonymous.org.uk> wrote:
>> > On 01/09/2011 22:50, Michael Busby wrote:
>> >> I have found the following and see that you can convert from raid4 to
>> >> raid0 fairly easy
>> >>
>> >>
>> >> http://ubuntuforums.org/showpost.php?p=10412231&postcount=20
>> >>
>> >> i have a 2 disk raid5 and want to be able to convert this to raid0, i
>> >> was thinking of adding a extra 2 disk and setting them up as raid0,
>> >> moving the data over then adding the original raid5 disks to the raid0
>> >> setup, but i see that you are unable to add disk to a raid0 setup,
>> >> would it be possible to setup a raid4 with 2 disks and 1 missing, move
>> >> the data from the raid5 to raid4 then add both of the original disks
>> >> to the raid4 the downgrade this to raid0???
>> >
>> > Off the top of my head, feeling slightly sozzled (been for a few beers),
>> > this might work, but as your linked post referring to a list reply from
>> > Neil Brown says, you should test first. You could use some USB sticks,
>> > or alternatively loopback devices are ideal for this kind of test.
>> >
>> > Cheers,
>> >
>> > John.
>> >
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>
>
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
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^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Raid5 to another raid level??
2011-09-02 9:12 ` Michael Busby
@ 2011-09-02 10:22 ` NeilBrown
2011-09-02 10:35 ` Michael Busby
0 siblings, 1 reply; 17+ messages in thread
From: NeilBrown @ 2011-09-02 10:22 UTC (permalink / raw)
To: Michael Busby; +Cc: john.robinson, linux-raid
On Fri, 2 Sep 2011 10:12:32 +0100 Michael Busby <michael.a.busby@gmail.com>
wrote:
> Thanks Neil
>
> Is there anyway back from raid0 to raid4 as i know once at raid0 i
> will no longer be able to add any disks, in theory i could change
> echo raid0 > /sys/block/md0/md/level,but this would require adding a
> missing disk to the raid4 at the same time, not sure how easy that
> would be todo
>
Yes, you can switch from RAID0 to RAID4 in much the same way as you switch
from RAID4 to RAID0.
You can then freeze/add-disk/change-size/unfreeze/wait/switch-back-to-RAID0
to add more devices.
mdadm-3.2.2 should be able to do all this for you. i.e. you ask it to --grow
a RAID and --add some disks at the same time, and it will do all the required
magic.
This hasn't been tested extensively, but should work in simple cases.
Of course the more devices you have in a RAID0, the less reliability you have
- but e.g. as a cache for a tape backup system a large RAID0 is fine.
NeilBrown
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Raid5 to another raid level??
2011-09-02 10:22 ` NeilBrown
@ 2011-09-02 10:35 ` Michael Busby
2011-09-02 12:49 ` NeilBrown
0 siblings, 1 reply; 17+ messages in thread
From: Michael Busby @ 2011-09-02 10:35 UTC (permalink / raw)
To: NeilBrown; +Cc: john.robinson, linux-raid
Great, will test that in a bit
will mdadm 3.2.2 support converting raid4 to raid5
"A RAID4 can change the number of devices or the size of individual
devices. It cannot be converted to RAID5 yet (though that should be
trivial to implement)"
On 2 September 2011 11:22, NeilBrown <neilb@suse.de> wrote:
> On Fri, 2 Sep 2011 10:12:32 +0100 Michael Busby <michael.a.busby@gmail.com>
> wrote:
>
>> Thanks Neil
>>
>> Is there anyway back from raid0 to raid4 as i know once at raid0 i
>> will no longer be able to add any disks, in theory i could change
>> echo raid0 > /sys/block/md0/md/level,but this would require adding a
>> missing disk to the raid4 at the same time, not sure how easy that
>> would be todo
>>
>
> Yes, you can switch from RAID0 to RAID4 in much the same way as you switch
> from RAID4 to RAID0.
> You can then freeze/add-disk/change-size/unfreeze/wait/switch-back-to-RAID0
> to add more devices.
>
> mdadm-3.2.2 should be able to do all this for you. i.e. you ask it to --grow
> a RAID and --add some disks at the same time, and it will do all the required
> magic.
>
> This hasn't been tested extensively, but should work in simple cases.
>
> Of course the more devices you have in a RAID0, the less reliability you have
> - but e.g. as a cache for a tape backup system a large RAID0 is fine.
>
> NeilBrown
>
>
>
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Raid5 to another raid level??
2011-09-02 10:35 ` Michael Busby
@ 2011-09-02 12:49 ` NeilBrown
2011-09-02 13:11 ` Michael Busby
0 siblings, 1 reply; 17+ messages in thread
From: NeilBrown @ 2011-09-02 12:49 UTC (permalink / raw)
To: Michael Busby; +Cc: john.robinson, linux-raid
On Fri, 2 Sep 2011 11:35:30 +0100 Michael Busby <michael.a.busby@gmail.com>
wrote:
> Great, will test that in a bit
>
> will mdadm 3.2.2 support converting raid4 to raid5
>
> "A RAID4 can change the number of devices or the size of individual
> devices. It cannot be converted to RAID5 yet (though that should be
> trivial to implement)"
I guess the man page needs updating. You would need a reasonably recent
kernel... 2.6.30 or later. I guess that isn't so recent any more.
NeilBrown
>
> On 2 September 2011 11:22, NeilBrown <neilb@suse.de> wrote:
> > On Fri, 2 Sep 2011 10:12:32 +0100 Michael Busby <michael.a.busby@gmail.com>
> > wrote:
> >
> >> Thanks Neil
> >>
> >> Is there anyway back from raid0 to raid4 as i know once at raid0 i
> >> will no longer be able to add any disks, in theory i could change
> >> echo raid0 > /sys/block/md0/md/level,but this would require adding a
> >> missing disk to the raid4 at the same time, not sure how easy that
> >> would be todo
> >>
> >
> > Yes, you can switch from RAID0 to RAID4 in much the same way as you switch
> > from RAID4 to RAID0.
> > You can then freeze/add-disk/change-size/unfreeze/wait/switch-back-to-RAID0
> > to add more devices.
> >
> > mdadm-3.2.2 should be able to do all this for you. i.e. you ask it to --grow
> > a RAID and --add some disks at the same time, and it will do all the required
> > magic.
> >
> > This hasn't been tested extensively, but should work in simple cases.
> >
> > Of course the more devices you have in a RAID0, the less reliability you have
> > - but e.g. as a cache for a tape backup system a large RAID0 is fine.
> >
> > NeilBrown
> >
> >
> >
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Raid5 to another raid level??
2011-09-02 12:49 ` NeilBrown
@ 2011-09-02 13:11 ` Michael Busby
2011-09-07 1:07 ` NeilBrown
0 siblings, 1 reply; 17+ messages in thread
From: Michael Busby @ 2011-09-02 13:11 UTC (permalink / raw)
To: NeilBrown; +Cc: john.robinson, linux-raid
I am using the 3.0.0 kernel so that should not be a issue, have just
upgraded mdadm on my box to 3.2.2 from 3.1.4
would i be right in thinking that to get from raid0 to raid5 i would
first have to change from raid0 to raid4 and add the extra disk for
parity, once i am at this level i would need a command to get the
parity data striped over the raid5 and not in a single disk like raid4
or maybe there is a way to go from raid0 direct to raid5 by adding the
extra disk and then having the parity data created and spread over the
disks....
On 2 September 2011 13:49, NeilBrown <neilb@suse.de> wrote:
> On Fri, 2 Sep 2011 11:35:30 +0100 Michael Busby <michael.a.busby@gmail.com>
> wrote:
>
>> Great, will test that in a bit
>>
>> will mdadm 3.2.2 support converting raid4 to raid5
>>
>> "A RAID4 can change the number of devices or the size of individual
>> devices. It cannot be converted to RAID5 yet (though that should be
>> trivial to implement)"
>
> I guess the man page needs updating. You would need a reasonably recent
> kernel... 2.6.30 or later. I guess that isn't so recent any more.
>
> NeilBrown
>
>
>>
>> On 2 September 2011 11:22, NeilBrown <neilb@suse.de> wrote:
>> > On Fri, 2 Sep 2011 10:12:32 +0100 Michael Busby <michael.a.busby@gmail.com>
>> > wrote:
>> >
>> >> Thanks Neil
>> >>
>> >> Is there anyway back from raid0 to raid4 as i know once at raid0 i
>> >> will no longer be able to add any disks, in theory i could change
>> >> echo raid0 > /sys/block/md0/md/level,but this would require adding a
>> >> missing disk to the raid4 at the same time, not sure how easy that
>> >> would be todo
>> >>
>> >
>> > Yes, you can switch from RAID0 to RAID4 in much the same way as you switch
>> > from RAID4 to RAID0.
>> > You can then freeze/add-disk/change-size/unfreeze/wait/switch-back-to-RAID0
>> > to add more devices.
>> >
>> > mdadm-3.2.2 should be able to do all this for you. i.e. you ask it to --grow
>> > a RAID and --add some disks at the same time, and it will do all the required
>> > magic.
>> >
>> > This hasn't been tested extensively, but should work in simple cases.
>> >
>> > Of course the more devices you have in a RAID0, the less reliability you have
>> > - but e.g. as a cache for a tape backup system a large RAID0 is fine.
>> >
>> > NeilBrown
>> >
>> >
>> >
>
>
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Raid5 to another raid level??
2011-09-02 13:11 ` Michael Busby
@ 2011-09-07 1:07 ` NeilBrown
0 siblings, 0 replies; 17+ messages in thread
From: NeilBrown @ 2011-09-07 1:07 UTC (permalink / raw)
To: Michael Busby; +Cc: john.robinson, linux-raid
On Fri, 2 Sep 2011 14:11:57 +0100 Michael Busby <michael.a.busby@gmail.com>
wrote:
> I am using the 3.0.0 kernel so that should not be a issue, have just
> upgraded mdadm on my box to 3.2.2 from 3.1.4
>
> would i be right in thinking that to get from raid0 to raid5 i would
> first have to change from raid0 to raid4 and add the extra disk for
> parity, once i am at this level i would need a command to get the
> parity data striped over the raid5 and not in a single disk like raid4
> or maybe there is a way to go from raid0 direct to raid5 by adding the
> extra disk and then having the parity data created and spread over the
> disks....
(I vaguely recall already replying to this but find no evidence - apologies
if this is a duplicate).
RAID0 to RAID5 does happen in two stages but only one rebuild is needed.
mdadm should make it all 'just work'.
i.e.
mdadm -G /dev/md0 -l 5 --raid-devices=4 --add /dev/sdf \
--backup-file=/root/md0-backup
This will:
- convert the array from RAID0 to RAID5 in a 'parity-last' layout, which
is really the same thing as RAID4.
- 'freeze' recovery
- add /dev/sdf as a spare
- request a reshape to change the layout from 'parity-last' to
'left-symetric'
- 'unfreeze' recovery
Then the kernel will notice that a reshape is needed and allowed, will add
the spare and start reshaping the array and creating parity at the same time.
So you don't need an intermediate state of a complete RAID4 - a degraded
RAID4 is sufficient and handled automatically.
NeilBrown
>
> On 2 September 2011 13:49, NeilBrown <neilb@suse.de> wrote:
> > On Fri, 2 Sep 2011 11:35:30 +0100 Michael Busby <michael.a.busby@gmail.com>
> > wrote:
> >
> >> Great, will test that in a bit
> >>
> >> will mdadm 3.2.2 support converting raid4 to raid5
> >>
> >> "A RAID4 can change the number of devices or the size of individual
> >> devices. It cannot be converted to RAID5 yet (though that should be
> >> trivial to implement)"
> >
> > I guess the man page needs updating. You would need a reasonably recent
> > kernel... 2.6.30 or later. I guess that isn't so recent any more.
> >
> > NeilBrown
> >
> >
> >>
> >> On 2 September 2011 11:22, NeilBrown <neilb@suse.de> wrote:
> >> > On Fri, 2 Sep 2011 10:12:32 +0100 Michael Busby <michael.a.busby@gmail.com>
> >> > wrote:
> >> >
> >> >> Thanks Neil
> >> >>
> >> >> Is there anyway back from raid0 to raid4 as i know once at raid0 i
> >> >> will no longer be able to add any disks, in theory i could change
> >> >> echo raid0 > /sys/block/md0/md/level,but this would require adding a
> >> >> missing disk to the raid4 at the same time, not sure how easy that
> >> >> would be todo
> >> >>
> >> >
> >> > Yes, you can switch from RAID0 to RAID4 in much the same way as you switch
> >> > from RAID4 to RAID0.
> >> > You can then freeze/add-disk/change-size/unfreeze/wait/switch-back-to-RAID0
> >> > to add more devices.
> >> >
> >> > mdadm-3.2.2 should be able to do all this for you. i.e. you ask it to --grow
> >> > a RAID and --add some disks at the same time, and it will do all the required
> >> > magic.
> >> >
> >> > This hasn't been tested extensively, but should work in simple cases.
> >> >
> >> > Of course the more devices you have in a RAID0, the less reliability you have
> >> > - but e.g. as a cache for a tape backup system a large RAID0 is fine.
> >> >
> >> > NeilBrown
> >> >
> >> >
> >> >
> >
> >
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^ permalink raw reply [flat|nested] 17+ messages in thread
* Raid5 to another raid level??
@ 2011-09-01 21:50 Michael Busby
2011-09-01 22:34 ` John Robinson
0 siblings, 1 reply; 17+ messages in thread
From: Michael Busby @ 2011-09-01 21:50 UTC (permalink / raw)
To: linux-raid
I have found the following and see that you can convert from raid4 to
raid0 fairly easy
http://ubuntuforums.org/showpost.php?p=10412231&postcount=20
i have a 2 disk raid5 and want to be able to convert this to raid0, i
was thinking of adding a extra 2 disk and setting them up as raid0,
moving the data over then adding the original raid5 disks to the raid0
setup, but i see that you are unable to add disk to a raid0 setup,
would it be possible to setup a raid4 with 2 disks and 1 missing, move
the data from the raid5 to raid4 then add both of the original disks
to the raid4 the downgrade this to raid0???
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Raid5 to another raid level??
2011-09-01 21:50 Michael Busby
@ 2011-09-01 22:34 ` John Robinson
0 siblings, 0 replies; 17+ messages in thread
From: John Robinson @ 2011-09-01 22:34 UTC (permalink / raw)
To: Michael Busby; +Cc: linux-raid
On 01/09/2011 22:50, Michael Busby wrote:
> I have found the following and see that you can convert from raid4 to
> raid0 fairly easy
>
>
> http://ubuntuforums.org/showpost.php?p=10412231&postcount=20
>
> i have a 2 disk raid5 and want to be able to convert this to raid0, i
> was thinking of adding a extra 2 disk and setting them up as raid0,
> moving the data over then adding the original raid5 disks to the raid0
> setup, but i see that you are unable to add disk to a raid0 setup,
> would it be possible to setup a raid4 with 2 disks and 1 missing, move
> the data from the raid5 to raid4 then add both of the original disks
> to the raid4 the downgrade this to raid0???
Off the top of my head, feeling slightly sozzled (been for a few beers),
this might work, but as your linked post referring to a list reply from
Neil Brown says, you should test first. You could use some USB sticks,
or alternatively loopback devices are ideal for this kind of test.
Cheers,
John.
^ permalink raw reply [flat|nested] 17+ messages in thread
end of thread, other threads:[~2011-10-12 16:01 UTC | newest]
Thread overview: 17+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2011-09-07 16:26 Raid5 to another raid level?? Michael Busby
[not found] ` <CAFsPQ__YdDnJw=qgLAq10vRbNPy4B_EhkV4FU0JAfovxnw9TxQ@mail.gmail.com>
2011-10-10 21:47 ` Michael Busby
2011-10-12 4:10 ` NeilBrown
2011-10-12 9:25 ` Michael Busby
2011-10-12 10:14 ` NeilBrown
2011-10-12 16:01 ` Michael Busby
-- strict thread matches above, loose matches on Subject: below --
2011-09-01 23:50 Michael Busby
2011-09-02 0:54 ` Michael Busby
2011-09-02 2:19 ` NeilBrown
2011-09-02 9:12 ` Michael Busby
2011-09-02 10:22 ` NeilBrown
2011-09-02 10:35 ` Michael Busby
2011-09-02 12:49 ` NeilBrown
2011-09-02 13:11 ` Michael Busby
2011-09-07 1:07 ` NeilBrown
2011-09-01 21:50 Michael Busby
2011-09-01 22:34 ` John Robinson
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